Communicating information over a communication medium, such as a cable or a radio channel, entails several challenges. Firstly, the information needs to be receivable at a receiver at a quality level that is appropriate for the application used. For example, where the information is a digital video, the communication rate, or bitrate, will typically be relatively high, and individual bit errors may be considered tolerable as a user is unlikely to notice them. On the other hand, where the information comprises digital files that are to be copied from the transmitter to the receiver, bit errors are not acceptable as the files would thereby become corrupted in transit. Error correction coding may be applied to detect and correct individual bit errors, such that a non-zero bit-error rate, BER, may be present with a zero block error rate, BLER.
Secondly, energy used in communicating the information should be sufficient to enable the communication at a sufficient quality level, but not an excessive quality level. For example in wireless communication, using excessive power in communication may cause interference in radio resources, which limits the overall capacity of the wireless communication system. For example, in code-division multiple access, CDMA, based wireless systems, many transmitting and receiving stations share the same frequency band, wherein communications effected using orthogonal codes appear as background noise to other stations. The higher the power used, the higher this noise level will appear to the other stations, and the other stations will need to use more power in their respective communications, further increasing the interference level. Of course, where communicating stations are battery-powered, using excessive transmit power will also drain battery resources unnecessarily quickly. Therefore, using a power level that is sufficient but not excessive is preferred.
Thirdly, feedback may be provided from a receiver to the transmitter to enable the transmitter to modify its transmission. For example, when a receiver determines that information is being transmitted at an unnecessarily high power, it may advise the transmitter, using feedback, that transmission power may be reduced. On the other hand, where a receiver determines that a bit and/or block error rate is too high, it may provide feedback advising the transmitter to increase transmit power.
Apart from, or instead of adapting transmit power, also other transmission parameters can be modified depending on the feedback. For example, modulation and coding parameters can be changed to better match the received signal quality.